Refrigeration system for well logging instruments



June 21, 1955 R, A. BERGAN REFRIGERATION SYSTEM'FOR WELL LOGGING INSTRUMENTSv Filed Aug. 30, 1952 .f Il

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ATTOTZINE-Y United States Patent O REFRIGERATION SYSTEM FOR WELL LOGGIN G INSTRUMENTS Reuben Allard Bergan, Tulsa, Okla., assignor to Well Surveys, Incorporated, Tulsa, Okla., a corporation kof Delaware This invention relates to the art of geophysical prospecting and more particularly to the art of radioactivity well logging utilizing a scintillation counter for detecting radiation. v

It is old in the art to log oil wells by measuring the natural radioactivity of the strata or by irradiating the strata adjacent the drill hole with fast neutrons or penetrating gamma radiation and simultaneously traversing the well with a gamma-ray or neutron detector or both. Such detectors have heretofore been of the type which employ a gaseous ionizable medium and produces electrical pulses or continuous current. The recently developed scintillation counters having solid or liquid detection media have certain advantages over the gaseous detectors of the prior art. Their greater density permits the use of a smaller size detector which is desirable in the small space available in a Well logging instrument; their low resolving time permits high speed counting; their high eiliciency provides a good signal-to-noise ratio; and their high stopping power is useful in gammaray and high-energy particle detection. Although the scintillation counter has desirable qualities for use in Well logging, it is diilicult to use, for it involves the use of iiuorescent media which operate unsatisfactorily under the high ambient temperatures found in oil wells, and the use of photosensitive surfaces which are subject to deterioration at temperatures above 170 F. Furthermore, high temperatures cause more thermal noise in the photo multiplier of the scintillation counter. The temperatures encountered in deep Wells may be as high as 400 F.

Attempts have been made to overcome difficulties arising from temperature elfects on conventional detectors.

These attempts have involved the use of solid insulators. These have not been entirely successful for even the best solid insulators permit heat conduction at too great a rate to be tolerated in radioactivity Well logging. There-is insuflicient space in a standard (S5/s O. D.) instrument to allow the use of enough solid insulation'to produce a great enough time-lag in change of temperature of critical elements.

All of the above enumerated difficulties apply with greater force to systems 'utilizing scintillation counters as the detecting elements. The instant invention overcomes these diiculties by providing novel means for producing a predetermined temperature environment for the scintillation counter and maintaining the environment at the chosen temperature.

This is accomplished by enclosing the photomultiplier tube and the scintillation medium in an insulating container, such as a Dewar ask, along with a thermal capacitance such as a capsule of Water. The Water is frozen by expanding a refrigerant in a heat exchanger disposed within the capsule. The heat exchanger is connected to a port in the external housing of the subsurface instrument. The port is provided so that refrigerant from an outside detachable source can be expanded into the heat exchanger and exhausted to the atmosphere or to the suction side of a compressor type refrigerating machine.

V2,711,084 Patented June 2l, .1955

The port is provided with a closure plug for usewhen the instrument isvlowered into the well. i

This invention eliminates the necessity for opening ther instrument in the field. It is undesirable to open delicate well logging equipment in the oil ield; any opening should be done in the laboratory under technical supervision. Furthermore, frequent opening may Wear and damage Huid-tight seals, and the more often the instruments are sealed, the greater the likelihood of leakage; any leakage of well fluid into the instrument will render the instrument inoperative. Even though no well fluid be permitted into the instrument housing, any opening of the housing may result in the contamination of the enclosed atmosphere, which must be kept clean and dry, especially when glass vacuum bottles are used. Glass vacuum bottles are delicate; moisture and other contaminants contributeto failure of glass, as well as electrical insulation. To ensure a proper atmosphere, the instrument is illed with dry, inert gas and sealed. If the atmosphere is to be maintained inert and dry, the instrument should not be opened except in the laboratory. v

In the preferred form of this invention the heat mayv be extracted from the instrument by the expansion of va refrigerant such as liquid carbon dioxide into the heat exchanger. The cool gas is Apassed through coils surrounded by water, thereby freezing the water.` The spent 1 Liquid carbon di` gas is exhausted into the outside air. oxide is especially suited for the purpose. It has a relatively high heat of vaporization at reasonable temperatures-approximately B. t. u./1b. at'32 lF. It is readily available everywhere at a moderate cos't. It is readilystored in commercial containers. It is non-poisonous and safe to handle. No auxiliary pumps or other mechanical or electrical equipment is necessary, for the container of liquid carbon dioxide may be coupledl'byV hose directly to the instrument housing. The container may be moved anywhere and is available for freezing the' water at the well head without removing the instrument from the logging cable for repeat runs.

Since the interior of the instrument must be'kept clean? f and free from water vapor, it is necessaryl to keep Vthe water for thermal capacitance in a sealed container. At' the same time, since water expands upon freezing, there must be room for expansion in the sealed container. In'- order that the water may be readily frozen with the instrument either vertical or horizontal, the water cham ber should be full of water. Therefore, the sealed container is divided by a piston into gas and Water chambers. Upon freezing of the Water, the piston moves to permit expansion, compressing the gas.

Therefore, the primary object of this invention is to provide a novel well surveying system. Another object is to provide a novel method and apparatus for cooling a scintillation counter logging instrument. Still another object is to provide in a well surveying subsurface instrument a heat exchanger and a thermal capacitance which can be rendered effective to cool the interior of the instrument from the exterior thereof without opening the instrument.

without` contamination of the interior of the instrument. Other objects and advantages of the present invention will become apparent from the following detailed descrip Still another object of this invention is to` provide cooling for a scintillation counter instrumenty the'strata surrounding' a Well or they are made by irradiating the strata with fast neutrons or penetrating gamma radiation and simultaneously detecting gamma radiation or neutrons thereupon coming from the strata. The scintillation counter may be used for radioactivity well logging, but it must be protected from the high temperatures found in many wells. In logging, the scintillation counter produces electrical pulses at a rate and of a sizedependent upon the incidentradiation. These pulses areamplified and sent to the surface over a cable. At the' surface the pulses may be further amplified. The rate of occurrence of pulses is recorded on aI recorder. as arfunction of the depth at which detection occurred, thereby producing a well log. In Figure l of the drawings there is illustratedl thedetector part of the subsurface instrument used in such a well logging system in which the refrigeration method of this invention is utilized.

The detector of radiation shown in Figure l comprises scintillation counter 1t) which consists of phosphor 11 and'photomultiplier 12. Power is supplied to photomultiplier 12 and output pulses are transmitted from photomult'iplier 12 through wires 13 and 14. The appliedV voltage is of the order of 1000 volts. The photomultiplier 12 includes the proper voltage divider for applying the proper voltages to the various dynodes of the photomultiplier tube. The scintillation counter is mounted rigidly in counter housing 15. The scintillation counter is' insulated from hot bore holes by the glass vacuum bottle y16. Since even the best insulation permits a lgradual` rise of temperature, thermal capacitance is necessa'ryto maintain a constant temperature.` Thermal capacitance is supplied in` the form of melting ice 17 also disposedl within the glass vacuum bottle. To prevent leakage of the water into the detector and onto the glass vacuum bottle,. the water is sealed in a container formed byy hollow cylinder 18 and seals 19 and 20. This water container isv fastened rigidly to the counter housing 15. The water container is divided into two parts by piston 21 which contines the water' to one part and gas to the other part. Movement of the piston to compress the gas as the? water expands upon freezing permits freezing of the water without breakage of the container or of the vacuum bottle. A diaphragm may be used'instead of the piston, or closed cell sponged rubber may replace the piston and gast chamber. Metallic cooling coil 22 is a heat exchanger by which heat is removed from the water in order tov freeze it. The coolant enters the cooling coil 22 through flexible tube 23 and is exhausted through exible tube 24. These tubes pass through solid insulator 25 which serves to insulate the open end of vacuum bottle 1 6.l

This` solid insulation may be of hair felt. Tubes 23 and 24F must be made of insulating material also. Rubber cushion 26 is placed between the bottom of vacuum bottle Y and its contents. The vacuum bottle is mounted on rubber cushions 27 and 28 within hollow cylinder 29 whichV isA part of the instrument housing exposed to the welll Cylinder 29' is made strong enough to withstand th'epressures found in deep wells. Plug 30 closes one end ofscylinder 29. The contents of cylinder 29 are firmly held in place by retaining ring 31. Hollow coupling 32 is: threaded tofasten securely to cylinder 29. Plug 33 closes theend of coupling32 to form a gas-tight chamber within cylinder 29 and coupling 32. Wires 13 and 14 are connected to electrical connector 34 which permits conduction ofthe power into the gas-tight chamber and pulse'sfro'm the g'astight chamber. Plugs 30 and 33 are pr-"ovideld with valves 35 and 36 respectively through which a' dry, inert atmosphere may be introduced and contaminants removed. This maintains an inert dry atmosphere in contact with the detector and the glass vacuum bottle.

To provide for the cooling of the scintallation counter, the water 17l isl frozen while the instrument is on the surface without opening the instrument housing to atmospheric contamination. The water is frozen by introducing liquid carbon dioxide through a port in the coupling it absorbsheat fromv thewater thereby freezing it. The

exhausted gas passes through tube 24 into the atmosphere.

After the water hasb'een frozen the high pressure tube 38 islremoved from; the fitting 39y and the orifice and exhaust vent are both sealed by a screw plug 40, shown in Figure Y 2, which seals the coolant tubeswhile the instrument is in the well'. This position of the orice results in Waste of cooling power forheatis absorbedbyr the cool gas from the orifice to the cooling coil 22 without doing useful work. The cooling system would operate more efficiently were tlie orice placed at the junction of tube 23 and cooling coill 22. However, this position would require dis` assembly oftheinstrument to-y clean or change the orifice. Furthermore, high pressure tubing and couplingsl are necessary where-the Carbon4 dioxide is in the liquid phase under pressure.

lin.- operationf a thermalv capacitance comprising 200 grams of ice hasbeen found to'be suflicient to log prac-` tically ally wellsy exhibiting high.v temperatures. With the present invention' this amount of ice can be frozen from a starting temperature of approximately 75 F. byusing l-iquid carbon dioxide at the same temperaturein from 8 to Al5 minutes. to eifect this freezing is approximately 2.3 pounds. `.Two hundred (200) grams of ice' enclosed within the Dewar flask along' with the scintillation counter willrnaintain the interior of vthe Dewar askat a temperaturefof approximately 45 F. for a period of about l0 hours in awe'll have an average temperature top to bottom thereof of approximately l=85 F. Thisis ample time to log a Y well 15,000 feet deep having atop hole temperature of approximately F. and a bottom hole temperature of approximately 560"L F; p

Althoughl the use of liquid carbon dioxide is described forv freezing the ice', other refrigerants such as ammonia may be passed through tubes 23 and 24 and cooling coil 22.-`

It` is to' be understood that this invention is not to be limited to-the specific modicat-ionsdescribed, but is to'be limitedl only by the following claims:

IA claim l. An apparatus for cooling' a Welllogging ydetector that comprises an instrument housing, thermal insulation disposed within said housing, said` detector disposed withinl said insulation,` a sealed container' also disposed within said insulation; movable meansv dividing said sealed container'in two parts, water disposedfwithin one of said tWO. parts, gasx disposed within thei other ofv said two parts, a,k

cooling coil disposed within said water, a source of refrigerant external to said instrument housing, sealed means for conducting said refrigerant from said source tosaid'f cooling coil', and sealed-means for conducting the.

spent refrigerant kfrom said` cooling coil to1 the outside of saidhousing.

2. An' apparatus for cooling av well logging detector that comprises a sealed' instrument housing, an inerti-and i dry atmosphere conned within said housing, thermal insulation also' disposed'within said housing, said detector disposedV within said'insu1ation,.a sealed container also disposed within` said insulation, water disposed within said sealed container, a coolingcoil also disposed within said' sealed container, a source of refrigerant external to said instrument housing',I sealed means for conducting said g refrigerant from said source .to said cooling coil, and sealed meansffon'conducting: the spent refrigerant from saidY coolingcoiltofthe outside of said housing.

3".y 15in' apparatus for" cooling" a1 wellv logging detector y The amount of carbon.- dioxide required that comprises an instrument housing, thermal insulation disposed within said housing, said detector disposed within said insulation, a sealed container also disposed within said insulation, water disposed Within said sealed container, expansion means to permit said water to expand Within said sealed container, a heat exchanger disposed in contact with said water, a source of refrigerant external to said instrument housing, sealed means for conducting said refrigerant from said source to said heat exchanger, and sealed means for conducting the spent refrigerant from said heat exchanger to the outside of said housing.

4. An apparatus for cooling a well logging detector that comprises an instrument housing, thermal insulation disposed within said housing, said detector disposed within said insulation, a sealed container also disposed Within said insulation, movable means dividing said sealed con tainer in two parts, thermal capacitance disposed within one of said two parts, gas disposed in the other of said two parts, a heat exchanger disposed in contact with said thermal capacitance, a source of refrigerant external to said instrument housing, sealed means for conducting said refrigerant from said source to said heat exchanger, and sealed means for conducting the spent refrigerant from said heat exchanger to the outside of said housing.

References Cited in the file of this patent UNITED STATES PATENTS 1,380,987 Lippincott .lune 7, 1921 1,870,696 Taylor Aug. 9, 1932 1,876,915 Gordon Sept. 13, 1932 2,016,377 Krotzer Oct. 8, 1935 2,324,103 Miller July 13, 1943 2,433,554 Herzog Dec. 30, 1947 2,671,323 Richert Mar. 9, 1954 2,686,268 Martin et al. Aug. 10, 1954 OTHER REFERENCES Solid Counters, Wouters ABCD-2203, August 5, 1948, published by the Atomic Energy Commission, Oak Ridge, Tennessee, pp. 1-5. 

